#include <bits/stdc++.h>
using namespace std;
double x, y, c;
bool k(double t)
{
	double h1 = sqrt(x * x - t * t);
	double h2 = sqrt(y * y - t * t);
	return c * (h1 + h2) - h1 * h2 > 0 ? 1 : 0;
}
int main(){
	while(scanf("%lf%lf%lf", &x, &y, &c) == 3)
	{
		double low = 0, mid;
		double high = min(x, y);
		while(low <= high)
		{
			mid = (low + high) / 2;
			k(mid) ? high = mid - 0.0001 : low = mid + 0.0001;
		}
		printf("%3lf\n", low);
	}
}